Describe the usefulness of blue-white screening, also called ?-complementation, in cloning vectors such as pUC19. Include in your answer the terms polylinker, DNA ligase, lacZ gene, insertional inactivation, Xgal, and ?-galactosidase
What will be an ideal response?
Answer: This is a powerful screening method, because white colonies contain a gene inserted into their plasmid whereas blue colonies do not. In the example of pUC19, the lacZ gene contains a polylinker site where the plasmid can be digested and have a foreign gene cloned into the site. The plasmid is re-circularized by DNA ligase such that now the lacZ gene and therefore β-galactosidase (LacZ) activity is disrupted. When transformed cells are grown on a medium with the artificial Xgal substrate, all of those without an insert will have a functional LacZ and will convert the Xgal to a blue color. A white colony suggests the cells contain an inserted gene within the lacZ gene of the plasmid, and these white colonies are likely to be the ones of interest.
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When these enzymes bind to a restriction site, they cut the DNA molecule into two molecules.
A. polymerases B. ligases C. restriction enzymes D. helicases
A cell with two of each kind of chromosome is called a
Which of the following is NOT a means of regulating gene expression?
A) Varying the rate at which messenger RNAs are translated B) Regulating how long a protein lasts in a cell C) Varying the rate at which messenger RNAs are transcribed D) Deleting genes from cells in which they are not needed E) Modifying proteins after they are synthesized
A. Define a gene
B. Consider two different species of yeast that have similar genome sizes. Is it likely that they contain the same number of genes? A similar number of chromosomes? What will be an ideal response?